In ordinary daily life, all kinds of lighting apparatus can be seen everywhere, such as fluorescent lamps, street lamps, table lamps, artistic lamps and so on. In the above-described lighting apparatus, the tungsten bulb is traditionally used as a light-emitting light source. In recent years, due to the ever-changing technology, light-emitting diode (LED) has been used as a light source. Moreover, in addition to lighting apparatus, for the general traffic signs, billboards, headlights etc., light-emitting diode has also been used as a light source. The light-emitting diode as a light source has the advantages of energy-saving and greater brightness. Therefore, it has been gradually common.
With the popularity of LED lamps, LED lamps are used in more and more occasions, but as we all know, LED lamps are powered by a dedicated LED power supply. As the user awareness of LED power deepens, the performance requirements of the LED power supply or lamp PF (Power Factor) and THD (Total Harmonic Distortion, THD) are also higher and higher. For example, DLC in the United States requires PF>0.9 for LED power supplies and THD<20%, and the similar requirements are in Europe. Therefore, for the general design of power supply, especially as a built-in power supply, the power supply needs to meet the requirements of more lamps as much as possible to reduce costs. Therefore, the load range of the power supply should be as wide as possible, and the minimum load can meet the requirements of PF>0.9 and THD<20%.